Lecture 13 - more cell division Flashcards
recap - 3 types of microtubules that form the mitotic spindle
kinetochore
interpolar
astral
what is the metaphase checkpoint
- all kinetochores must each be attached to a spindle
SPINDLE ASSEMBLY CHECKPOINT
what is the metaphase checkpoint
- all kinetochores must each be attached to a spindle
SPINDLE ASSEMBLY CHECKPOINT (SAC)
what is Mad2
protein kinase
part of SAC complex at the kinetochore
what does the SAC do
generates a stop signal at the kinetochore
how does SAC get inhibited
the stop signal is only inhibited once kinetochore attaches to MT
then SAC proteins removed by dyenin
what exactly is the stop signal produced by SAC
SAC makes APC inhibitor
APC is anaphase promoting complex
so naturally
SAC inhibits anaphase
since APC is blocked
how does APC work
covalently binds to ubiquitin
this ubiquitin tags proteins to get degraded
M-cdk
and securin
what would inhibiting Mad2 do
cytokinesis without anaphase
(even if there are no MT, still cytokinesis)
cuz cell cant tell that the kinetochores are unattached
what are cohesins cleaved by in anaphase
protease called seperase
when is separase activated
when SAC is fully inactivated
how does securin get degraded
via ubiquination and protasome
how does separase get activated
via active APC
and remember, APC can only be activated once SAC stops
and then once the separase is active it can go on to degrade cohesins
what is anaphase A
sister chromatids get split, move towards the spindle poles
staying attached to kinetochore MTs which depolymerise = making them shorter in one direction pulling the chromatids to one end
what is anaphase B
Spindle poles move further apart
what creates the pushing force in anaphase B
kinesin Eg-5 which creates a sliding force between the MTs from the opposite poles
the interpolar MTs continue growing at plus ends
what creates the pulling force in anaphase B
dyenin anchored in the cell cortex (thin network of actin filaments and actin-binding proteins that underlies the plasma membrane)
pulls the MT towards ends
telophase specfic events
nuc envelope and nuc lamins reassemble
golgi reassembles
secretion and endocytosis restart
what filaments form the contractile ring
actin and myosin ring
dynamic, so gets smaller around middle of the spindle
what is different about plant cells
no centrosomes
no dyenin
spindle poles are broad = minus end directed kinesins
what is used to make the plant cell membrane and cell wall
golgi derived vesicles
